1. Field of the Invention
The present invention relates generally to a method and apparatus for allocating frequency resources in a Cognitive Radio (CR) wireless communication system, and in particular, to a method and apparatus for dynamically selecting frequency resources for frequency resource allocation.
2. Description of the Related Art
The rapid development of wireless communication systems and the emergence of a variety of services are a driving force behind the increasing demand for radio resources. However, radio resources, i.e. the frequency spectrum, has come to be seen as a public asset and managed under strict governmental regulations. Multiple applications have already occupied much of commercially available spectrum, which makes it difficult to deploy a new wireless communication system.
As a solution to this problem, CR has been proposed. The CR technology senses an allocated but unused frequency band and shares the frequency band efficiently.
The CR technology is promising for application to future-generation wireless communications under study. A wireless communication system adopting CR is called a “CR system”.
If a primary system is to use a frequency band that the CR system now uses, the CR system has to immediately give it to the primary system. The primary system is a licensed wireless communication system legally authorized to use the frequency.
Therefore, it is critical to continue providing an ongoing service to Customer Premise Equipments (CPEs) in the CR system, despite the above situation. A CPE is defined as a terminal capable of communicating with a CR Base Station (BS). It is a generic term referring to a device that enables a user device to connect to a communication line of a public communication service provider. The BS communicates with the CPEs via a radio interface based on the CR technology and controls communications within its coverage area.
FIG. 1 illustrates an exemplary case of local interference in a typical CR system.
Referring to FIG. 1, a CR BS 100 supports point-to-multipoint communications and manages CPEs 101 to 106 that want to receive a CR service. A primary BS 110 is within a primary system and manages primary users 111 to 116.
The primary BS 110 and the CR BS 100 are not aware of the existence of each other, although they operate in the same frequency band. The primary user 116 (user A) serviced by the primary BS 110 is free of interference from the CR BS 100.
In contrast, when the CPE 102 (user B) receives downlink data from the CR BS 100, it is affected by a downlink signal from the primary BS 110. Also, uplink data directed from user B to the CR BS 100 may interfere with user A.
If the downlink frequency band of the CR system is in a poor status or the signal strength of the primary system is greater than that of the CR system under a CR environment, communications may be impossible for the CPEs serviced by the CR system.